The present invention relates to a freezable coolant composition or, more particularly, to an inexpensive but efficient freezable coolant composition having a freezing point substantially higher than 0.degree. C. reaching around room temperature and capable of exhibiting a great cooling capacity by virtue of a relatively large latent heat of fusion and a relatively large specific heat to be useful, for example, as a coolant in an air conditioner using "an economical ice".
As is known, a great variety of cooling or chilling agents are employed heretofore for keeping a material at a relatively low temperature for a duration with an object of, for example, freshness preservation of foods and so on depending on the nature of the material to be kept at the low temperature or the temperature at which the material is to be kept.
The cooling agents under current use can be classified into two types depending on the working principle of the cooling agent including those of the latent-heat type such as ice and certain organic compounds melting at the cooling temperature and those of the sensible-heat type such as certain metals and inorganic compounds utilizing mere heat absorption without any phase changes.
As compared with the sensible-heat type cooling agents working within a temperature range involving no phase change of the substance, the cooling agents of the latent-heat type in general working within a temperature range involving the solid-liquid phase change of the substance exhibit a large cooling capacity by virtue of utilization of the latent heat of fusion which is usually greater than the specific heat of the same substance so that a large cold-keeping effect can be obtained with a relatively small amount of the latent-heat type cooling agent. The temperature range in which a latent-heat type cooling agent works can be narrow enough for the large cooling capacity so that the thermal loss with the ambience can be minimized as a great advantage. Japanese Patent Kokai 62-62192 proposes specific halogenated hydrocarbon compounds, alcoholic compounds having 2 to 10 carbon atoms in a molecule, ketone compounds and ether compounds as well as aqueous solutions of inorganic salts as a latent-heat type cooling agent.
Even by setting aside the ice/water system as a matter of course, the freezing temperature range of most of the latent-heat type cooling agents in the prior art is at or in the vicinity of 0.degree. C. so that they are not suitable as a refrigerant in an air conditioner. When a cooling temperature substantially higher than 0.degree. C. is desired as an optimum storage temperature for certain foods, for example, no latent-heat type cooling agent working within such a temperature range is available in the prior art. Other problems in the conventional latent-heat type cooling agents or coolant compositions in general include their not so large latent heat of fusion and specific heat as not to ensure a desirable large cooling capacity, long-term stability to withstand deterioration and safety from the risk of environmental pollution. The sensible-heat type cooling agents are, as is mentioned above, generally not comparable with the latent-heat type cooling agents in respect of the small specific heat not to exhibit a large cooling capacity.